A. Field of the Invention
This invention relates to the operation of a communication network, and more particularly relates to a method and apparatus for powering components on the communication network.
B. Description of Related Art
The universal serial bus (USB) is a protocol for a serial bus. USB supports data exchange between a host computer and a wide range of simultaneously accessible peripherals. The attached peripherals share USB bandwidth through a host scheduled token based protocol. The USB allows peripherals to be attached, configured, used and detached while the host and other peripherals are in operation.
The USB transfers signal and power over a four wire cable with two wires for power (+5 Volts) and ground and the other two wires for data signaling. The USB in one configuration is 12 megabits per second and supports up to 128 devices. One of the purposes behind the universal serial bus is to provide ease of use to add PC peripherals. The USB is designed to handle a broad range of devices such as telephones (both analog, digital, and proprietary), modems, printers, mice, joysticks, scanners, keyboards, and tablets. Therefore, removed from the personal computer are the parallel, serial, graphics, modem, sound/game and mouse ports. The USB is designed so that external devices, such as a mouse or a keyboard may be correctly detected and properly configured upon attachment. Ordinarily, the topology of the USB system is tiered star. At each star is a universal serial bus repeater providing power for the devices, routing of signals in each direction and providing terminations for each line.
The universal serial bus repeater is a device which has one upstream port, a universal serial bus controller, and several downstream ports. The upstream port is toward the host, such as connected to a computer or other data communication device, and the downstream ports is toward a device. The universal serial bus controller performs the following functions: routing of the signals from the upstream port to the downstream ports and from the downstream ports to the upstream port; and error detection and recovery. The universal serial bus controller supports two power source modes (bus-powered or self-powered). Ordinarily, if the power required for the downstream ports and embedded functions is equal to or less than the power the bus can supply, the universal serial bus controller can be powered by the bus. If the power required for the downstream ports and embedded functions is more than what the bus can supply, the universal serial bus controller and the downstream ports are self-powered.
When the universal serial bus controller is self powered, the operator of the system must follow a special sequence in configuring the system. The operator must first connect the power source for the universal serial bus controller and the downstream ports. Then, the operator must connect the universal serial bus controller to the port on the computer. Otherwise, if the bus is connected to the universal serial bus controller without the universal serial bus controller being powered, the computer may determine that there is a problem with the universal serial bus controller since the computer detects that the universal serial bus controller is connected, but it is not responding due to a lack of power. Thus, the sequence of connecting the power supply and then the connector to the bus must be followed to avoid any potential errors.
Further, all self-powered universal serial bus controllers should implement overcurrent and thermal error protection for safety reasons. The universal serial bus controller should have a way to detect faults in the system such as an overcurrent or thermal error condition and report it to the universal serial bus software. Should the aggregate current drawn by a single downstream port or group of downstream ports exceed a preset value or the thermal value of the power supply be too high, the power should be removed from the downstream ports and the condition should be reported through the universal serial bus controller to the computer. Fault detect circuits, detecting overcurrent and thermal errors, are used to protect from catastrophic device failures, software errors that turn on devices when the current budget has been exceeded, and operator actions such as shorting out the connector pins. Known overcurrent limiting methods include poly fuses, standard fuses, or a solid state switch.
Moreover, the power supply which supplies power to the universal serial bus controller and the downstream ports in the self-powered mode are designed either with expensive power switches such as power transistors or switching chips. In this manner, the power which is supplied by the power supply can be turned on upon power up or turned off when an overcurrent is detected. Also, the power can be turned on or turned off by the software on the computer through the universal serial bus controller, which is contained within the universal serial bus controller.
Finally, when the universal serial bus controller and the downstream ports are in the self-powered mode, this limits the overall operation of the system. In the event of an overcurrent thermal error or other condition which requires the power supply to be removed, the power to the universal serial bus controller is removed as well. Thus, in order to have a reliable universal serial bus system, the power to the universal serial bus controller and the downstream ports should be reliable. It would therefore be desirable to have an improved method and apparatus for powering components on the communication network.